Athletic training, particularly when combined with weight loss, increases a woman's risk of anovulation, irregular menses, and amenorrhea. The underlying cause of training-associated abnormalities in GnRH pulsation is unknown; however, it has been hypothesized that changes in estrogen metabolism and body composition may contribute to training-associated abnormalities in GnRH pulsation. The purpose of this study is to assess changes in estrogen metabolism and body composition using radiometric analysis.